1. Field of the Invention
This invention relates to a coordinate input apparatus in which the coordinate input can calibrated.
2. Description of the Related Art
In recent years, a system which recognizes input handwritten characters, figures, etc. has attracted attention as the system that will play the role of the next-generation man-machine interface (hereinafter referred to as MMI). In this kind of handwriting recognition system, a configuration is often employed such that a coordinate input apparatus and a display apparatus are positioned so as to overlap and the trace of a hand-written character or figure as it is displayed on the display apparatus. Such a configuration enables a character or a figure to be input exactly as if writing a note on paper.
A coordinate input apparatus which accepts data input by indicating on a tablet surface by means of a pen-like pointer is an indispensable input apparatus for use in a handwriting recognition system. Such an input apparatus accepts data input as the writing trace of a character or figure, and is also used for the indication and selection of icons and menus which are displayed on a screen or in a printed form in the environs of a screen. The selection of such icons or menus, by indicating, is a switch for starting the execution of a function or process corresponding to its icon or menu, so an icon or menu displayed on a screen is hereinafter called a soft switch.
Although a coordinate input apparatus and a display apparatus have coordinate systems separate from each other, in the case of a one-piece type configuration as mentioned above, respective coordinate systems need to be matched. What is more, coordinate systems of a coordinate input apparatus differ from one system to another, and therefore a calibration operation for matching coordinate systems is generally performed for each set. It is natural that this calibration operation be performed before shipment and at assembly time in a factory. Taking into account the secular change in the coordinate system of the coordinate input apparatus, it is made to be performed by the user.
Traditionally, this kind of calibration operation was performed as described below. This is shown in FIG. 9. FIG. 9(A) is an outer appearance of an electronic calculator which can input from a display screen. FIG. 9(B) is a view illustrating that a display section 92 and a coordinate input section 93 are formed in one piece. Now, when calibration operation start is instructed by pressing the calibration key 97 of the keyboard 91 shown in FIG. 9(A), a symbol for illustrating a press point is displayed on a specific point (e.g., 95, 96) in the display section 92. The operator indicates position, by pressing with the pen 94 directly onto this symbol. Such action is repeated for a plurality of points on a screen. The CPU (not shown) calculates the correction parameter from the difference between the display coordinate in the display section 92 and the detection coordinate in the coordinate input section 93 and stores it in a non-volatile storage section or the like. After this, correction is made by the above-mentioned parameter on the detection coordinate in the coordinate input section 93 and it is made a final input coordinate value. At this calibration operation time, if the operator erroneously indicates, by pressing, a position different from a display position, correct calibration cannot be made, and in the worst case, an input coordinate deviates greatly or is distorted and the coordinate input section 93 becomes inoperable. In such a case, as shown in FIG. 9, an electronic apparatus having a keyboard 91 can issue the instruction to start a calibration operation by means of a calibration key 97. However, an electronic apparatus having no input sections other than a coordinate input section, namely, an apparatus which inputs all indications by using icons displayed on a screen, has a problem in that if the coordinate input section becomes inoperable, nothing can be input, including the instruction to recalibrate. In recent years, because some users have an aversion to the keyboard, an electronic apparatus having no main input sections other than a coordinate input section in which the above-mentioned character recognition technology is adopted has attracted attention from the viewpoint of MMI. A method of reliably calibrating an input coordinate position in the coordinate input section of this kind of apparatus has been desired.